SURGICAL INSTRUMENT

A surgical instrument comprises an inner tube which rotates within an outer tube and carries a surgical tool that includes a burr for cutting tissue exposed to the burr through an opening in the outer tube. The instrument includes several features which enhance the efficiency at which tissue fragments severed by the burr are aspirated through the inner tube, and which enable the burr to effectively cut relatively soft tissue as well as harder tissue such as bone. For example, the burr includes a proximal shank having a wall that has an aperture therein with a substantial width relative to an outer diameter of the wall for conveying tissue fragments cut by the burr into an interior chamber of the shank, and thence into a passage in the inner tube. The opening in the outer tube is axially elongated sufficiently to expose a major portion of the aperture. The large aperture and its exposure by the outer tube opening reduce the risk of clogging by admitting larger tissue fragments into the inner tube for aspiration. Additionally, the burr includes a plurality of grooves that are axially elongated and inclined transversely to the flutes, and the grooves define a plurality of axially spaced notches in each of the cutting edges. The notches divide the cutting edges into relatively small segments that produce correspondingly small tissue fragments (even when the burr is used to cut soft tissue) to further reduce the risk of clogging. In addition, the cutting edges are preferably provided with a positive rake that makes the cutting edges sharper and suitable for effectively cutting, rather than tearing or shredding, relatively soft tissue.